Space use by foraging Galápagos penguins during chick rearing

Between May 2004 and May 2005, we studied the horizontal and vertical movements of foraging Galapagos penguins Spheniscus mendiculus during their breeding season to examine space use at sea and to compare the volume of water exploited by this penguin to those of other penguin species. A total of 23 adult penguins (11 males and 12 females) brooding chicks were fitted with GPS- depth recorders at the 3 main nesting sites on south-western Isabela Island. Birds moved between 1.1 and 23.5 km (mean = 5.2 ± 4.9 km) from the nest, concentrating foraging in a strip of sea within 1.0 km of the shore. Foraging trips lasted a mean of 8.4 ± 2.0 h. Although the deepest dive was 52.1 m, birds spent, on average, 90% of their time underwater at depths less than 6 m. Both foraging ranges and dive depths were below those predicted from allometric regressions derived from other penguin species. Applying the maximum values for movement to calculate space use, the Galapagos penguin exploits a maximum volume of water of <1.4 km 3 , which is almost 90 times less than that predicted for its mass, and thus utilises only a small portion of the total potentially available upwelling area within the Galapagos Archipelago.